Multiply More Fractions

10 min

Narrative

The purpose of this Number Talk is for students to demonstrate strategies and understandings they have for using the properties of operations when multiplying whole numbers and mixed numbers. These understandings help students develop fluency and will be helpful later in this lesson when students will flexibly multiply.

Launch

  • Display one problem.
  • “Give me a signal when you have an answer and can explain how you got it.”
  • 1 minute: quiet think time
Teacher Instructions
  • Record answers and strategy.
  • Keep problems and work displayed.
  • Repeat with each problem.

Student Task

Find the value of each expression mentally.

  • 6×386 \times \frac {3}{8}
  • 6×2386 \times 2 \frac {3}{8}
  • 7×9107 \times \frac {9}{10}
  • 7×39107 \times 3 \frac {9}{10}

Sample Response

  • 188\frac {18}{8} or 2282 \frac {2}{8}: I multiplied 6 and 3 and had that many eighths.
  • 142814 \frac {2}{8}: 6×26 \times 2 is 12 so I added that to the product from the first problem.
  • 6310\frac {63}{10} or 63106 \frac {3}{10}: I multiplied 7 and 9 and had that many tenths.
  • 2731027 \frac {3}{10}: 7×37 \times 3 is 21 so I added 21 to the product previous problem.
Activity Synthesis (Teacher Notes)
  • Display the last problem.
  • “If someone found 7×47 \times 4 first, what might they do next?” (Subtract 7×1107 \times \frac{1}{10} since 39103 \frac{9}{10} is 110\frac{1}{10} less than 4.)
Standards
Addressing
  • 5.NF.4·Apply and extend previous understandings of multiplication to multiply a fraction or whole number by a fraction.
  • 5.NF.B.4·Apply and extend previous understandings of multiplication to multiply a fraction or whole number by a fraction.

20 min

15 min